Washington is not sure how the documents posted on the social media platform Telegram last week were made public, White House spokesperson John Kirby told reporters on Monday.
It is unclear whether the files were leaked or hacked.
“The president remains deeply concerned about any leakage of classified information into the public domain. That is not supposed to happen and it’s unacceptable when it does,” Kirby said.
The classified documents include an analysis of satellite imagery of Israeli military activities.
The files said the Israeli military “handled” air-launched ballistic missiles – which are fired from an aircraft – and conducted covert drone activities earlier this month “almost certainly” for a strike on Iran.
But the assessment, which appears to have been prepared by the National Geospatial-Intelligence Agency, added that the analysis cannot “definitively predict the scale and scope”.
Several US media outlets cited anonymous US officials saying the secret documents seem authentic.
The files first appeared on the Telegram channel Middle East Spectator, which publishes news and commentary about the region. The account shares messages that support Iran and its allies, but has refuted claims of ties to the government in Tehran.
US House Speaker Mike Johnson confirmed on Sunday that an investigation into how the documents became public is “underway, ” saying he will receive a briefing on the matter.
